The present invention relates to adjustable wobble dado assemblies for cutting elongate grooves of varying widths. More particularly, the invention relates to an improvement to existing wobble dado assemblies which enables such assemblies to cut grooves of varying widths having cross sections more accurately rectangular in shape than can be obtained with the use of existing conventional adjustable wobble dado assemblies.
Adjustable wobble dado assemblies in various forms have long been used in the wood-working trades, as exemplified by those shown in the following U.S. patents:
U.S. Pat. No. 682,810 PA0 U.S. Pat. No. 716,094 PA0 U.S. Pat. No. 2,286,633 PA0 U.S. Pat. No. 2,458,216 PA0 U.S. Pat. No. 2,544,814 PA0 U.S. Pat. No. 2,665,722 PA0 U.S. Pat. No. 2,922,449 PA0 U.S. Pat. No. 3,172,437 PA0 U.S. Pat. No. 3,848,512 PA0 U.S. Pat. No. 4,055,204.
All of such wobble dado assemblies have adjustable hub assemblies for fixedly mounting a blade upon an arbor and adjustably tilting the axis of the blade at various angles with respect to the arbor to cut elongate grooves of varying widths. When adjusted for cutting the narrowest possible groove, the blade axis of such a dado assembly is normally not tilted with respect to the arbor but rather is oriented so as to be coaxial with the arbor. At such a blade orientation, a narrow groove substantially rectangular in cross section can be cut. However, as the axis of the blade is tilted to assume progressively greater angles relative to the arbor for cutting progressively wider grooves, the cross sections of the grooves become increasingly nonrectangular. In such case the bottoms of the elongate grooves assume a concave, arcuate cross-sectional shape, as depicted in FIG. 7 as well as some of the more accurately-drawn prior art patents such as U.S. Pat. Nos. 2,665,722 and 3,172,437. As the grooves become wider, the nonrectangularity of their cross sections becomes so prominent that the use of such wobble dado assemblies becomes unsatisfactory for precise wood-working.
Another source of inaccuracy in prior art adjustable wobble dado assemblies is the multiplicity of separate parts in their adjustable hub assemblies. As shown in the aforementioned patents, it is normal for such adjustable hub assemblies to include both inner and outer tapered adjustment rings or discs on each side of the blade, all separate from the blade and interposed between the blade and the surfaces of the arbor to which the blade is fixed. Such multi-piece structures create at least four interface surfaces between separate parts within the hub assembly where tolerance errors can accumulate, affecting the tilt of the blade. These accumulated tolerance errors are magnified at the locations of the cutting teeth in proportion to the magnitude of the blade's radius, thereby causing inaccuracies and inconsistencies in the width dimension of the groove formed by the teeth. One prior art structure, i.e. that shown in U.S. Pat. No. 2,922,449, has a lesser number of separate components in its hub assembly due to the fact that the blade is stamped with a deformed thin central section lying at an angle to the plane of the blade, thereby eliminating the need for the separate inner rings or discs employed in other prior art structures. However, a central section of this type introduces another source of inaccuracy because of the natural tendency of such a thin section, created by high pressure deformation, to warp.
Accordingly, what is needed is an adjustable wobble dado assembly which is capable of cutting elongate grooves with greater accuracy, both with respect to their desired rectangular cross-sectional shapes and with respect to their dimensions.